Over the course of more than a decade, numerous publications have appeared, and numerous patent applications have been filed, relating to the objective and usefulness of utilizing rubber powders, and to possible processes for their preparation.
The reason for the constantly increasing interest in pulverulent rubbers is readily understandable in view of the current state of the processing technology of the rubber industry. The situation is that, to this day, rubber mixtures are produced with high expenditure of time, heat energy consumption and high personnel requirements. The main reason for this is that the rubber raw material is provided in the form of bales.
The comminution of the bales and the intimate mixing with fillers, mineral oil plasticizers and vulcanization auxiliaries are carried out on mills or in internal mixers. To avoid deterioration of quality, the mixture is prepared in several process steps. In general, the mixture is stored between these steps. The internal mixers or mills are followed by extruder-pelletizers or extruder-roller dies.
Only a completely novel processing technology can lead away from this highly unsatisfactory and expensive rubber processing technique. In the course of recent years, the use of free-flowing rubber powders has therefore been discussed increasingly. These offer the possibility of processing rubber mixtures in a simple and rapid manner, like thermoplastic powders.
Very recently, several ways of preparing pulverulent free-flowing rubber-filler mixtures, preferably rubber-carbon black mixtures, based on all-purpose rubbers, have been found and described (compare German Patent Applications P 21 35 266.9 [U.S. Pat. No. 3,846,365], P 22 14 121.5 [U.S. Pat. No. 3,895,035], P 22 60 340.3 [3,920,604], P 23 24 009.7 [U.S. Pat. No. 3,945,978], P 23 25 550.7 [U.S. Pat. No. 3,922,240], P 23 32 796.0 [U.S. Pat. No. 3,929,707], P 24 39 237.8 [U.S. Pat. No. 4,073,755] and P 26 54 358.8 [U.S. Pat. No. 4,138,375]). The essential characteristics of the prior art processes described in these applications are the use of particular surface-active compounds and the use of an expensive, at times multi-stage, precipitation technique.
However, as mentioned, the main object of using powder rubbers is to improve the economics of rubber processing. Thus, the foregoing processes do not meet the precondition for the success of such endeavors, i.e., the inexpensive preparation of rubbers in powder form.